Rainfall in Arid Areas vs. Deserts

Definitions and Rainfall Amounts

• Deserts: By common definitions, deserts receive less than 250mm (10in) of precipitation per year. Some of the driest deserts, like the Atacama or certain parts of the Sahara, see close to zero annual rainfall, sometimes going years without measurable precipitation12345.

• Arid Areas: "Arid" broadly encompasses deserts but can sometimes refer to slightly wetter, but still very dry, environments. Arid regions are defined as areas with severe lack of water, typically less than 250mm (10in) of annual precipitation, similar to deserts. Some classification systems break this down further:

  • Hyper-arid: <100mm (4in) per year67.

  • Arid (true desert): 100-250mm (4-10in) per year1897.

  • Semi-arid: 250-500mm (10-20in) per year. These transition toward more moderate climates and are not considered true deserts110.

Comparison Table

Region Type	Annual Rainfall	Example Locations
Hyper-arid	<100mm (4in)	Atacama Desert, central Sahara67
Arid/Desert	100–250mm (4–10in)	Most deserts: Sahara, Gobi, Arizona1245
Semi-arid	250–500mm (10–20in)	Sahel (Africa), steppes in Asia110

Key Differences

• Rainfall in deserts is almost always less than 250mm/10in per year, making them the driest arid areas. Some can have virtually zero precipitation for years at a time.

• Arid regions include deserts but may also refer to areas on the drier side of semi-arid zones, with rainfall up to—but not exceeding—250mm (10in). Semi-arid regions may look desert-like but receive enough rainfall (10–20in/250–500mm) for shrinkage-resistant vegetation and occasional pasturing.

Notes

• Precipitation in both arid and true desert regions is highly variable, often occurring in a few brief, intense storms, and is frequently accompanied by high evaporation rates3.

• Deserts can occur not just in hot climates but in cold ones as well (e.g. the polar deserts), provided the precipitation remains below the arid threshold82.

In summary, deserts are a subset of arid regions, defined by their extremely low annual rainfall. All deserts are arid, but not all arid areas are deserts, as some arid climates receive slightly more rainfall than typical deserts but nowhere near enough to support lush vegetation or consistent agriculture168.

1. https://www.nps.gov/subjects/geology/arid-landforms.htm
2. https://en.wikipedia.org/wiki/Desert_climate
3. https://www.britannica.com/science/desert/Environment
4. https://earthobservatory.nasa.gov/biome/biodesert.php
5. https://www.desertmuseum.org/books/nhsd_desert
6. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/aridity
7. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/arid-land
8. https://www.worldatlas.com/articles/what-is-an-arid-climate.html
9. https://library.fiveable.me/key-terms/ap-enviro/arid-climates
10. https://ucmp.berkeley.edu/exhibits/biomes/deserts.php
11. https://www.fao.org/4/t0122e/t0122e03.htm
12. https://www.climatetypesforkids.com/arid-climate
13. https://www.climate.gov/news-features/feed/natural-variability-behind-recent-desert-rainfall-increases
14. https://www.frontiersin.org/research-topics/45022/extreme-precipitation-in-arid-regions-observation-mechanisms-and-simulations/magazine
15. https://eos.org/research-spotlights/understanding-rare-rain-events-in-the-driest-desert-on-earth
16. https://www.taylorfrancis.com/chapters/edit/10.1201/9780203971307-7/rainfall-arid-semi-arid-regions-%E2%80%94jetse-kalma-stewart-franks
17. https://www.ebsco.com/research-starters/earth-and-atmospheric-sciences/rain-shadow-deserts
18. https://kids.nceas.ucsb.edu/biomes/desert.html